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Kilauea Volcano's east rift zone eruption continues: most lava travels through tubes from the vent area to the coast
This update current as of November 18, 1997[Eruption updates are posted approximately every two weeks. More frequent updates will accompany drastic changes in activity or increased threat to residential areas.]
For readers familiar with events of the past few months, recent changes include these:
- The vent inside Pu`u `O`o rarely spills across the crater floor. Instead the top of the magma column remains 10-20 m below the bounding rampart. Magma in the vent circulates below the crusted lava surface of the crater floor--out of our sight except from the air.
- Lava from the south shield travels in tubes to the coast, an in-tube distance of about 10 km. Travel time for a particle of melt is probably about 3 hours from vent to ocean. Eruption rate is generally 500,000-600,000 cubic meters per day. Although lava will escape occasionally from the tube to form new surface flows, no such breakouts have occurred in the past four weeks.
- Ocean entries remain situated at East Kamokuna and Waha`ula, which are the distal ends of the tube system. At East Kamokuna, a bench collapse in early November lopped off 4.75 acres (1.92 hectares). Since then, new lava from the beheaded tube is building a shelf at the foot of the new cliffs created by the collapse. Steam plumes rise as a nearly continuous curtain from the 500-m-long edge of the slowly prograding lava flow.
- Sulfur dioxide gas emissions from vents in the Pu`u `O`o area remain high, about 2,800 tons per day but spiking as high as 5,000 tons per day.
- For Big Island residents and visitors, the second symposium on Vog and Laze (volcanic smog and lava haze) will be held November 22 in Kona. The first symposium, November 8 in Hilo, was attended by about 85 people. Details for the November 22 meeting are listed at the end of this report.
The 55th episode of Kilauea's almost 15-year-long east rift zone eruption continues. This episode, which began February 24, 1997, was characterized in its early months by shifting vent locations on the west and southwest flanks of Pu`u `O`o cone and by rapid enlargement of the episode 50-55 lava shield. The flow field expanded slowly until, in July, lava reached the sea. The supply of lava to these flows became restricted to tubes, and surface flow activity diminished greatly.
Oblique aerial photo looking southwest from Pu`u `O`o's north rim. Silvery flows in foreground are east-directed overflows from August and October; photo p0398 taken Nov. 14, 1997. Distance is 200 m between north summit (high point on right) and south summit (hidden in fume on left). Crater vent lies at base of dense fume cloud in Pu`u `O`o Crater. South shield is heavily fuming area south (left) of the cone.
During the last 15 weeks, eruptive activity has been concentrated at two main vents: the "crater vent" on the Pu`u `O`o crater floor and the "south shield," a lava shield about 300 m south of the Pu`u `O`o cone. The most obvious of these has been "crater vent," which originated as a spatter cone. In September, however, the spatter cone subsided into its own throat, leaving a pit. The pit is slowly enlarging and now is about 60 m in diameter. Lava froths and sloshes within this cauldron. All of these changes occurred within the already existing crater of Pu`u `O`o.
In the two weeks prior to November 3, magma issued nearly continuously from the throat of crater vent, spilling eastward to the main crater floor. This activity has diminished greatly in the past two weeks. Instead, the lava rarely tops the rampart that bounds the vent. It does circulate away from the vent, but most of the activity is hidden beneath the crust of the crater floor. The limited extent of incandescent lava has reduced the magnificent nighttime glow that was so prominent from many vantage points on the east slope of Kilauea volcano.
Near-vertical aerial photo looking southwest at Pu`u `O`o; photo p0407 taken Nov. 14, 1997. Incandescent glow is top of magma column in the crater vent within Pu`u `O`o cinder-and-spatter cone. Periodic spills from the vent coat the main crater floor. East rim of main crater is near bottom of photo, and silvery flows there mark the main-crater overflow from October. Topographic relief in the crater results mainly from drainback into cracks within the crater floor, but also from subsidence, which creates the low escarpments cutting the crater-mantling lava. Cross-crater width is 250 m at greatest breadth.
Across-crater view looking southeast at Pu`u `O`o (photo p0387 taken Nov. 14, 1997). Sharp ledge on east rim is overflow lava from August and October 1997; distance from camera to ledge is 250 m. Varicolored foreground surface is north rim, which lies about 11 m higher than the overflow surface. Depth to crater floor is about 50 m.
The other main vent, south shield, is the source of the flows entering the ocean at the Waha`ula and East Kamokuna sites near the east boundary of Hawai`i Volcanoes National Park. The flows are encased within lava tubes for most of their length and are visible only through skylights in the roof of the tube.
The tubes discharge their lava at the shoreline. The hot lava, about 1,150 degrees Celsius when it reaches the ocean, generates dense plumes of steam upon contact with seawater. The new lava builds benches beyond the low seacliffs that bound the south coast of the Big Island.
View southwest across coastal plain, showing lava benches at Waha`ula (landward of steam plume at left) and East Kamokuna (at right). Distance between plumes is about 970 m. These benches are new land built since July 1997. Photo p0372, Nov. 14, 1997.
Small explosions periodically disrupt the rapidly chilling lava and throw it onto the bench, constructing low nearshore (littoral) cones. These small explosions pose a minor threat for visitors. A far greater threat exists, however; these benches may collapse into the sea without warning, triggering large steam explosions that hurl dense rock and molten spatter tens of meters inland.
Such a collapse occurred in early November (two weeks ago), lopping 4.75 acres (1.92 hectares) of existing episode-55 bench off and into the ocean at East Kamokuna. (No one was on the bench, so only land, not life, was lost.) Since then, a new lava flow from the beheaded tube is building a shelf at the foot of the new cliffs created by the collapse. These features may be discernible in the previous photo. The righthand steam plume is at East Kamokuna. The new lava flow, 40-50 m wide, is adjacent on the right side of that steam plume. The word "cliffline" and a white leader point to the cliff that formed as a result of the collapse. Thus, the new lava flow is filling an embayment created during the abrupt destruction of unstable land. Steam plumes rise as a nearly continuous curtain from the 500-m-long edge of the slowly prograding lava flow.
The situation just described should serve as ample warning: No one should venture onto the benches, no matter how stable the new land may appear.
Eruption-viewing opportunities change constantly, so those readers planning a visit to the volcano should contact Hawai`i Volcanoes National Park for the most current eruption information (808-985-6000). Additional photographs and descriptions of east rift eruptive activity may be found on the University of Hawai`i's web site.
On Sunday, November 16, east Hawai`i and especially Hawai`i Volcanoes National Park were engulfed in one of the worst episodes of vog this year. Gentle southeasterly winds blew much of the sulfur dioxide (SO2) emissions from Kilauea's east rift zone--about 2800 tons per day (t/d)--directly across the heavily visited Kilauea caldera area of the National Park. The SO2 emission rate of 2800 t/d is about 40 percent higher than the average for the last several years during continuous eruption. Summit SO2 emissions from Kilauea remain in the range of 50-100 t/d.
The poor air quality produced the fourth exceedence of the EPA 24-hour primary health standard this year and caused the National Park Service to close their Headquarters facilities at the summit. Park employees were sent to the coast for a breath of fresh air. Telephone complaints about the vog were received from as far away as Oahu (330 km). Vog on the east side of the Big Island comprises mainly noxious SO2 gas and acidic sulfate particles (aerosols). In contrast, most of the gas component has been converted to sulfate particles to form vog along the Kona coast (west side of Big Island) and elsewhere in the state.
If you are a Big Island resident or visitor who wishes to learn more about vog and its effects on health, agriculture, equipment, and air quality, consider attending a Vog and Laze Symposium being presented by the Center for the Study of Active Volcanoes. The symposium will be held in Kona on November 22 at the Kona Surf Hotel in the Kamehameha Ballroom.
The symposium begins at 9 a.m., with presentations by scientists and health professionals who will discuss the composition of vog and laze and its impact on the community. An informal discussion and resource booths will also be featured. This is the second of two admission-free symposia sponsored by a grant from the Federal Emergency Management Agency. For additional information call (808)-974-7631 (Hilo, Hawai`i).
This map current as of November 18, 1997
Eruption-viewing opportunities change constantly, refer to the HVO home page for current information. Those readers planning a visit to Kilauea or Mauna Loa volcanoes can get much useful information from Hawai`i Volcanoes National Park.
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